Alternator AC ripple waveform

Vehicle details:
Nissan Navara NP300
Year: 2015
Engine: YS23DDTT
Model: D23

Fault:
1. Alternator fault/warning light comes on intermittently. During this time, the alternator is not charging (measured 12.71V). 
2. The engine idle also drops as if a cylinder has been deactivated.
3. The battery sometimes also drains overnight resulting in the vehicle having to be jump started.

Numbers 1 & 2 only last for a few minutes and then everything returns to normal. By normal I mean the alternator fault/warning light turns off, the alternator starts charging & the engine idles back up to normal rpm.

Have only managed a ripple test at this point in time so am wanting to know if the waveform is good/normal. I only have Picoscope traces as a reference but from my perspective there is either a lot of noise in the scope trace(s) OR the diode(s) are playing up (second waveform video makes me think so). Would be good to get a second opinion.

Thanks.


(forgot to use trigger for a more stable trace)

FYI below is my Picoscope reference waveform for PWM alternator:

Bumping thread to see if anyone has some feedback on scope trace...

Thanks

It's hard to get a look at what is going on, in your video.  I recommend zooming in on your voltage and time-sweep. Also, you can set a trigger to try and stabilize the waveform.

Re-captured scope trace, first video is me going through time & voltage scales but as you can see using a trigger on the final waveform doesn't really stabilize it:



Second video I found a function to produce somewhat of a clearer waveform:



@ Chad are you able to see what's happening now?

I don't see any any sign of a bad diode, or excessive ripple. I welcome other opinions, though. What  is the amplitude/voltage difference, between the peaks and valleys, of the wave? It looks to be much less than 500mv,  about 100mv if I am seeing it correctly. You can increase the electrical load ( high beams, blower, on high, windshield wipers, etc ) to see if it increases the Amplitude. It doesn't look like the prettiest ripple I have ever seen. But, I don't think I would condemn the alternator based on it, alone.

2. The engine idle also drops as if a cylinder has been deactivated.

Low RPM can cause an alternator to not charge.  When this happens, can you increase the RPM and make it charge, again.

3. The battery sometimes also drains overnight resulting in the vehicle having to be jump started.

I would look into this. Do you know how to test for, and track down, parasitic draws. If it leads you to the alternator, then you have your answer.

Yeah I too am seeing an amplitude of 100mV. I’ll scope the alternator again tomorrow to see what happens to the amplitude when extra electrical load is turned on.

About the drain, it’s a 2015 model so amp clamping the battery cable and then pulling fuses is a no go. I reckon I’ll have to measure the voltage drop across the fuses while the car is asleep.

With regard to the engine idle drop:
The engine idle drops when the battery warning light comes on. When this happens the alternator stops charging completely. I scoped the PWM ECU control terminal at the alternator (it’s a 3 pin regulator) and it measures a constant 6V both when the alternator is not charging and when everything magically returns back to normal and the alternator starts charging again. Because of this I’m inclined to believe that it is an intermittent alternator issue. 

That being said, when the alternator is charging, and the AC & lights are turned on I expect to see a duty cycle/square wave but the scope trace stays at a constant 6V suggesting a 100% duty cycle @ idle? Also tried revving the engine, with electrical loads on, to get a square wave going but a constant 6V trace is all I got.

@ Chad, I'm also considering the alternative scenario that the battery warning light & alternator not charging are caused from the engine idle rpm dropping.

Thanks Chad for feedback. Input from anyone else would be great too.